As the proportion of senior citizens in the entire population increases at a rapid rate in recent years, an increasingly large number of newly built houses are based on barrier-free design. According to the concept of barrier-free design, no step-like discontinuity exists between adjacent living spaces, and a home elevator is often installed so as to allow the occupant to move from one floor level to another without descending or ascending stairways.
Senior citizens may be mostly capable of walking short distances but are often unable to walk to remote destinations.
Under such circumstances, there have been a significant amount of demand for motor-powered wheelchairs for home use which are suitable for lightly disabled people such as senior citizens. More conventional and widely used motor-powered wheelchairs are designed for more highly disabled people, and are normally large in size and not very maneuverable.
Based on such a consideration, KK Unicam or one of the co-applicants of this application previously developed a wheelchair for home use which comprises a body frame equipped with a pair of drive wheels, and caster wheels arranged to the front and rear of the drive wheels so as to allow the wheelchair to be turned while remaining at a stationary point, and announced it in the Journal of the Japan Society of Orthotics & Prosthetics, Vol. 9, No. 2 (1993).
This wheelchair for home use is capable of turning at a stationary position and compact in size so that it can be turned in a tight space such as an elevator cage without being interfered by the walls of the elevator cage. Also, the diameter of the drive wheels is significantly reduced for a high maneuverability.
However, as this wheelchair for home use developed by KK Unicam or one of the co-applicants of this application is adapted to ride over a step by lifting the front caster wheels by making use of the rearward inertia force resulting from a sudden forward movement of the wheelchair, the following problems were found as the wheelchair rides over a stepped part of the floor.
(1) the user experiences some discomfort from the sudden acceleration of the wheelchair; PA1 (2) the wheelchair must often come to a sudden stop after riding over a stepped part of the floor to avoid collision with wall surfaces, in particular in narrow passages: and PA1 (3) a special mode of operation is required when riding over a stepped part of the floor which may not be easy to execute for a senior individual. PA1 (1) When the front caster wheel runs into a stepped portion of a floor surface as the wheelchair moves forward, the first link member turns around the point of connection between the body frame and the first link member so as to reduce the distance between the front caster wheel and the drive wheels while, at the same time, the front end of the body frame tilts upward around the rear caster wheel. The front caster wheel thereby lands on the upper surface of the step, and successfully rides over the step. PA1 (2) When the rear caster wheel runs into a stepped portion of a floor surface as the wheelchair moves backward, the second link member turns around the point of connection between the body frame and the second link member so as to reduce the distance between the rear caster wheel and the drive wheels while, at the same time, the rear end of the body frame tilts upward around the front caster wheel. The rear caster wheel thereby lands on the upper surface of the step, and successfully rides over the step.
The present invention was made in view of such problems, and has its primary object to provide a wheelchair which can travel over stepped floor surfaces without causing discomfort to the user while allowing the diameter of the drive wheels to be minimized for maximum maneuverability.